The invention is directed to a speed gear device for the crank-wheel of bicycles and similar vehicles.
1. Field of the Invention
The invention belongs to the technical field of commodities for bicycles and similar engines.
2. Description of the Prior Art
It is a well-known fact that the speed gear devices for the crank-wheel of bicycles and similar vehicles consist chiefly of a fork with two sides or limbs between which the chain is passed, and of a hinged parallelogram mechanism or the like for the transverse shifting of said fork, so that the chain will be brought upon the sprocket of the crank-wheel which has been selected for driving the vehicle. The mechanism is actuated by the driver using a hand lever and cable system, or a lever system, or other similar device.
A first disadvantage is that it is often difficult for the driver to accurately place the control hand lever or lever in the angular position corresponding to a correct transverse shifting of the chain in order to bring the latter in the correct winding position on the selected sprocket wheel. When the chain is not located correctly, the operation becomes noisy, damages may occur, and the chain may come off, which makes it necessary to adjust it back again.
A further disadvantage, as may be seen in FIG. 1 of the drawings, resides in the fact that chain (A) is passed between the sides (B1-B2) of the fork which is designated generally by reference letter (B). The chain will be shifted transversely and wound around one of the sprockets (C-D) of the crank-wheel of the bicycle, in order to modify the gear ratio and the driving action, this in conjunction with the winding of the chain around one of the sprockets (E-F-G-H-I . . . ) of the free wheel wedged to the hub (J) of the rear wheel of the bicycle. On account of the number of the free wheel sprockets, and also due to the fact that the crank-wheel is equipped with at least two sprocket wheels, the chain (A) tends to occupy slanting positions which have a very substantial inclination relative to the planes of the sprocket wheels. The result is that friction of the chain against either one of the sides (B1-B2) of the fork is produced, thereby producing a quick wearing off and damaging of the fork sides and the chain, unpleasant rubbing and noises, multiple and repetitive hammering of the ends of the chain links against the sides of the fork.